享元模式:运用共享技术有效地支持大量细粒度的对象。
内部状态:在享元对象内部并且不会随环境改变而改变的共享部分。
外部状态:随环境改变而改变的,不可以共享的
如果一个应用程序使用了大量的对象,而大量的这些对象造成了很大的存储开销时就应该考虑使用;
还有就是对象的大多数状态可以外部状态,如果删除对象的外部状态,那么可以使用相对少的共享对象取代很多组的对象,此时可以考虑使用。
享元对象本身也耗费资源,另外,为了使该对象可以共享,需要将一些状态外部化,这使得程序的逻辑复杂化,因此,应当在有足够多的对象实例可供共享时才值得使用。
class Program
{
static void Main(string[] args)
{
int extrinsicstate = 22;
FlyweightFactory f = new FlyweightFactory();
Flyweight fx = f.GetFlyweight("X");
fx.Operation(--extrinsicstate);
Flyweight fy = f.GetFlyweight("Y");
fy.Operation(--extrinsicstate);
Flyweight fz = f.GetFlyweight("Z");
fz.Operation(--extrinsicstate);
UnsharedConcreteFlyweight uf = new UnsharedConcreteFlyweight();
uf.Operation(--extrinsicstate);
Console.Read();
}
}
class FlyweightFactory
{
private Hashtable flyweights = new Hashtable();
public FlyweightFactory()
{
flyweights.Add("X", new ConcreteFlyweight());
flyweights.Add("Y", new ConcreteFlyweight());
flyweights.Add("Z", new ConcreteFlyweight());
}
public Flyweight GetFlyweight(string key)
{
return ((Flyweight)flyweights[key]);
}
}
abstract class Flyweight
{
public abstract void Operation(int extrinsicstate);
}
class ConcreteFlyweight : Flyweight
{
public override void Operation(int extrinsicstate)
{
Console.WriteLine("具体Flyweight:" + extrinsicstate);
}
}
class UnsharedConcreteFlyweight : Flyweight
{
public override void Operation(int extrinsicstate)
{
Console.WriteLine("不共享的具体Flyweight:" + extrinsicstate);
}
}